Introduction to Web - Lecture Notes PDF

Introduction to web Lecture 1-Basic concepts Dr. Heba Mamdouh Minia university Faculty of science Computer science department Internet  What is Internet? It can be defined in many ways as follows: is a world-wide global system of interconne...

Introduction to web Lecture 1-Basic concepts Dr. Heba Mamdouh Minia university Faculty of science Computer science department Internet  What is Internet? It can be defined in many ways as follows: is a world-wide global system of interconnected computer networks. A collection of computer networks that use a protocol to exchange data. Internet uses the standard Internet Protocol (TCP/IP). Every computer in internet is identified by a unique IP address. Internet is accessible to every user all over the world. Advantages and Disadvantages  Intranet A private network contained within an organization or business used to share information and resources among coworkers.  Internet vs. Intranet Intranet Internet Localized Network. Worldwide Network Doesn't have access to Intranet Have access to Internet. More Expensive Less Expensive More Safe Less Safe More Reliability Less Reliability  Extranet A private network that securely shares part of an organization’s information or operations with external partners. Extranet refers to network within an organization, using internet to connect to the outsiders in controlled manner. It helps to connect businesses with their customers and suppliers and therefore allows working in a collaborative manner. Extranet  Extranet vs. Intranet Extranet Intranet Internal network that can be Internal network that can not accessed externally. be accessed externally. Extranet is extension of Only limited users of a company's Intranet. company. For limited external Only for communication within communication between a company. customers, suppliers and business partners.  Network Overview Network two or more computers connected together for the purpose of communicating and sharing resources  Networks LAN – Local Area Network Usually confined to a single building or group of buildings. Is a group of computer and peripheral devices that are connected in a limited area such as school, laboratory, home, or office building. WAN – Wide Area Network Usually uses some form of public or commercial communications network to connect computers is widely dispersed geographical areas.(internet) 11  LAN vs. WAN LAN WAN Whereas WAN stands for Wide Area LAN stands for Local Area Network. Network. But WAN’s ownership can be private or LAN’s ownership is private. public. The speed of LAN is high(more than While the speed of WAN is slower than WAN). LAN. Whereas the propagation delay in WAN is The propagation delay is short in LAN. long(longer than LAN). While it’s design and maintenance is LAN’s design and maintenance is easy. difficult than LAN. LAN covers small area i.e. within the While WAN covers large geographical building. area. Whereas WAN uses PSTN or satellite link Transmission medium used in LAN is co- as a transmission or communication axial or UTP cable. medium.  The Client/Server Model Client/Server can describe a relationship between two computer programs – the "client" and the "server". Client requests some type of service (such as a file or database access) from the server. Server fulfills the request and transmits the results to the client over 14 a network The Internet Client/Server Model Client – Web Browser Server – Web Server 15  World Wide Web (WWW) It consists of a vast assortment of files and documents that are stored on computers ( servers) and written in some form of Hypertext Markup Language (HTML) that tells browsers how to display the information. A technical definition of the World Wide Web is : all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP). Internet and Web is not the same thing: Web uses internet to pass over the information World Wide Web (WWW)  WWW Operation WWW works on client- server approach. Following steps explains how the web works: 1. User enters the URL (say, http://www.yahoo.com) of the web page in the address bar of web browser. 2. Then browser requests the Domain Name Server for the IP address corresponding to http://www.yahoo.com. 3. After receiving IP address, browser sends the request for web page to the web server using HTTP protocol which specifies the way the browser and web server communicates. 4. Then web server receives request using HTTP protocol and checks its search for the requested web page. If found it returns it back to the web browser and close the HTTP connection. 5. Now the web browser receives the web page, It interprets it and display the contents of web page in web browser’s window.  Web Page web page is a document available on world wide web. Web Pages are stored on web server and can be viewed using a web browser. A web page can contain huge information including text, graphics, audio, video and hyper links. These hyper links are the link to other web pages. Collection of linked web pages on a web server is known as website. There is unique Uniform Resource Locator (URL) is associated with each web page.  Web Browser is an application software that allows us to view and explore information on the web. User can request for any web page by just entering a URL into address bar. Most common web browser available today: Browser Vendor Internet Explorer Microsoft Google Chrome Google Mozilla Firefox Mozilla Opera Opera Software Safari Apple  How Browsers Display Web pages When a Web page is opened in a browser, the browser reads and interprets the HTML file and formats the Web page for display. If there are references to external files, such as images or multimedia, these files are downloaded from the server and displayed in the browser window. It is important to note that HTML files are text files that only contain references to the external files – you do not “embed” these files into the Web page.  Web server Web server is a computer where the web content is stored. Web site is collection of web pages while web server is a software that respond to the request for web resources.  How Web Server Working When client sends request for a web page, the web server search for the requested page: if requested page is found then it will send it to client with an HTTP response. If the requested web page is not found, web server will the send an HTTP response: Error 404 Not found. If client has requested for some other resources then the web server will contact to the application server and data store to construct the HTTP response.  IP Address IP address can be identified as: is a unique logical address assigned to a device over the network. is a unique set of numbers which identifies a computer location. An IP address exhibits the following properties: IP address is 32 bits (4 bytes) long. IP address consists of two components: network component and host component. Each of the 4 bytes is represented by a number from 0 to 255, separated with dots. 28 For example 137.170.4.124  Domain Name  Locates an organization or other entity on the Internet.  A domain name becomes your Business Address so care should be taken to select a domain name. Your domain name should be easy to remember and easy to type.  A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can 29 locate a computer by a name.  Domain Extension Types There are many types of domain extensions you can choose for your domain name. This depends on your business nature. For example, if you are going to register a domain name for education purpose then you can choose.edu extension..com − Stands for company/commercial, but it can be used for any website..net − Stands for network and is usually used for a network of sites..org − Stands for organization and is supposed to be for non-profit bodies..us,.in − They are based on your country names so that you can go for country specific domain extensions.biz − A newer extension on the Internet and can be used to indicate that this site is purely related to business..info − Stands for information. This domain name extension can be very useful, and as a new comer it's doing well..tv − Stands for Television and are more appropriate for TV channel sites. The Domain Name System The Domain Name System (DNS) associates Domain Names with IP addresses. DNS translates the domain name into IP address automatically. Browser: http://google.com IP Address: 173.194.116.72  Uniform Resource Locator (URL) Identifier for the location of a document on a web site The protocol part tells the web browser how to handle the file. Similarly we have some other protocols also that can be used to create URL are: FTP 33 https  Internet Protocols Protocols Rules that describe the methods used for clients and servers to communicate with each other over a network. There is no single protocol that makes the Internet and Web work. A number of protocols with specific functions are needed. 34  FTP: File Transfer Protocol A set of rules that allow files to be exchanged between computers on the Internet. Web developers commonly use FTP to transfer web page files from their computers to web servers. FTP is also used to download programs and files from other servers to individual computers. 35  E-mail Protocols Sending E-mail SMTP: Simple Mail Transfer Protocol Receiving E-mail POP (POP3): Post Office Protocol IMAP: Internet Mail Access Protocol 36  HTTP - Hypertext Transfer Protocol  A set of rules for exchanging files such as text, graphic images, sound, video, and other multimedia files on the Web.  Web browsers send HTTP requests for web pages and their associated files.  Web servers send HTTP responses back to the web browsers. 37  Basic Web Programming HTML CSS JavaScript For more Dynamic Web Programming we use e.g., ASP.NET SQL AJAX PHP etc.  References HTML Tutorial: http://www.w3schools.com/html CSS Tutorial: http://www.w3schools.com/css JavaScript Tutorial: http://www.w3schools.com/js